Los Angeles - The Seattle Sounders preserved their unbeaten start to the Major League Soccer season on Saturday, sending Toronto FC spinning to their first loss of the campaign with a 3-2 win at CenturyLink Field.

Two goals from striker Will Bruin helped the Sounders to all three points to keep them firmly in the hunt at the top of the Western Conference alongside pace-setting Los Angeles F.C.

Seattle and Toronto, who met in back-to-back MLS Cup finals in 2016 and 2017, were two of the last four remaining undefeated teams heading into this week's round of fixtures.

Toronto drew first blood after only 11 minutes, when United States international Jozy Altidore nodded home Alejandro Pozuelo's cross at the far post to put the visitors 1-0 ahead.

But Seattle's midfield gradually began to carve out openings and Bruin levelled in the 24th minute when he calmly headed Brad Smith's deflected cross past Toronto goalkeeper Quentin Westberg for 1-1.

Bruin added his second in the 66th minute, tucking away a low finish from Smith's cross after good work by Uruguayan playmaker Nicolas Lodeiro down the left flank.

Cristian Roldan put Seattle 3-1 ahead two minutes later, latching onto a perfectly weighted through ball from defender Kevin Leerdam before lifting his finish over Westberg and into the roof of the net.

Altidore pulled a goal back in the 70th minute to complete a flurry of scoring, but Toronto were unable to find a way through Seattle's defence for the remainder of the contest.

Seattle head coach Brian Schmetzer believes his team's strong start to the season can be traced back to last year's playoffs, when they exited to Portland in a penalty shoot-out.

"Last year they knew they were very good and they didn't achieve their objective," Schmetzer said.

"The narrative with Toronto after (losing MLS Cup in) 2016 was they had something to prove," Schmetzer added.

"I think being that good last year, had we gotten past Portland, I think we had as good a chance as anybody at getting to the final again. That little bit of motivation might have had some carryover."